U.S. patent number 9,832,083 [Application Number 15/288,123] was granted by the patent office on 2017-11-28 for apparatus and method for detecting channel spacing and system.
This patent grant is currently assigned to FUJITSU LIMITED. The grantee listed for this patent is FUJITSU LIMITED. Invention is credited to Liang Dou, Zhenning Tao, Ying Zhao.
United States Patent |
9,832,083 |
Zhao , et al. |
November 28, 2017 |
Apparatus and method for detecting channel spacing and system
Abstract
Embodiments of the present disclosure provide an apparatus and
method for detecting channel spacing and a system. The apparatus
for detecting channel spacing includes a first estimating unit
configured to estimate a frequency offset of a center channel
according to a received signal, a second estimating unit configured
to estimate a frequency offset of a neighboring channel according
to the received signal, and a determining unit configured to
determine channel spacing according to the frequency offset of the
center channel estimated by the first estimating unit and the
frequency offset of the neighboring channel estimated by the second
estimating unit. With the embodiments of the present disclosure,
estimation accuracy of channel spacing may be ensured, and
influence of non-ideal factors on estimation value may be
reduced.
Inventors: |
Zhao; Ying (Beijing,
CN), Dou; Liang (Beijing, CN), Tao;
Zhenning (Beijing, CN) |
Applicant: |
Name |
City |
State |
Country |
Type |
FUJITSU LIMITED |
Kawasaki |
N/A |
JP |
|
|
Assignee: |
FUJITSU LIMITED (Kawasaki,
JP)
|
Family
ID: |
58500220 |
Appl.
No.: |
15/288,123 |
Filed: |
October 7, 2016 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20170104643 A1 |
Apr 13, 2017 |
|
Foreign Application Priority Data
|
|
|
|
|
Oct 10, 2015 [CN] |
|
|
2015 1 0651905 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04B
10/00 (20130101); H04B 10/07957 (20130101); H04L
43/028 (20130101); H04L 7/0087 (20130101) |
Current International
Class: |
H04L
12/26 (20060101); H04L 7/00 (20060101); H04B
10/079 (20130101); H04B 10/00 (20130101) |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Huang; David S
Attorney, Agent or Firm: Staas & Halsey LLP
Claims
The invention claimed is:
1. An apparatus for detecting channel spacing, comprising: a memory
that stores a plurality of instructions; and a processor coupled to
the memory and configured to execute the instructions to: estimate
a frequency offset of a center channel according to a received
signal; estimate a frequency offset of a neighboring channel
according to the received signal; and determine channel spacing
according to the frequency offset of the center channel estimated
by the first estimating unit and the frequency offset of the
neighboring channel estimated by the second estimating unit.
2. The apparatus according to claim 1, wherein the processor
further executes the instructions to: preprocess the received
signal, and estimating unit estimate the frequency offset of the
center channel and the frequency offset of the neighboring channel
according to the preprocessed received signal.
3. The apparatus according to claim 1, wherein the apparatus
further comprises: a filter configured to filter the received
signal, and the processor further executes the instructions to:
estimate the frequency offset of the center channel and the
frequency offset of the neighboring channel according to the
filtered received signal.
4. The apparatus according to claim 3, wherein the filter:
configured to set a filter bandwidth of the center channel, filter
the received signal according to the filter bandwidth of the center
channel, and provide the filtered signal to the processor; and
configured to set filter bandwidth of the neighboring channel,
filter the received signal according to the filter bandwidth of the
neighboring channel, and provide the filtered signal to the
processor.
5. The apparatus according to claim 4, wherein the filter bandwidth
of the neighboring channel is set to ensure that information on the
neighboring channel is maintained and information on the center
channel is removed in a case where the channel spacing or the
frequency offset of the neighboring channel or the frequency offset
of the center channel change.
6. The apparatus according to claim 1, wherein the apparatus
further comprises: a synchronizer configured to perform
synchronization operations on the received signal, and the
processor further executes the instructions to: estimate the
frequency offset of the center channel and the frequency offset of
the neighboring channel according to the synchronized received
signal.
7. The apparatus according to claim 6, wherein the synchronizer
further: configured to perform a first synchronization operation on
the received signal, where the processor estimates the frequency
offset of the center channel according to the synchronized received
signal; and configured to perform a second synchronization
operation on the received signal, where the processor estimates the
frequency offset of the neighboring channel according to the
synchronized received signal.
8. The apparatus according to claim 1, wherein the processor
further executes the instructions to: estimate the frequency offset
of the center channel and/or the frequency offset of the
neighboring channel according to the following formula:
.DELTA.f=angle(<S.sub.nS.sub.n+k*>)/2.pi.kT.sub.s; where,
S.sub.n is complex information on an n-th sampling point,
S.sub.n+k* is complex conjugate information on an (n+k)-th sampling
point, and T.sub.s is a sampling period, n, k and n+k are integers
which are less than the number of sampling points.
9. The apparatus according to claim 1, wherein the processor
further executes the instructions to: estimate the frequency offset
of the center channel and/or the frequency offset of the
neighboring channel according to the following formula:
.DELTA.f=angle(<S.sub.nS.sub.n+N*>)/2.pi.NT.sub.s.DELTA.f=angle(<-
;S.sub.nS.sub.n+k*>)/2.pi.kT.sub.s; where, S.sub.n is complex
information on a periodic signal or an n-th symbol of a training
sequence, S.sub.n+N* is complex conjugate information on an
(n+N)-th symbol, T.sub.s is a symbol period, and N is the number of
symbols of each period, n is an integer which is less than the
number of symbols.
10. A method for detecting channel spacing, comprising: estimating
a frequency offset of a center channel according to a received
signal; estimating frequency offset of a neighboring channel
according to the received signal; and determining channel spacing
according to the estimated frequency offset of the center channel
and the estimated frequency offset of the neighboring channel.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the priority benefit of Chinese Patent
Application No. 201510651905.X filed on Oct. 10, 2015 in the
Chinese State Intellectual Property Office, the disclosure of which
is incorporated herein in its entirety by reference.
BACKGROUND
1. Field
The present disclosure relates to the field of communications, and
in particular to an apparatus and method for detecting channel
spacing and a system.
2. Description of the Related Art
In a multicarrier optical communication system, subcarrier data are
modulated in several optical carriers independent of each other.
Under an ideal condition, wavelengths of lasers are stable, and
spacing of the carriers are fixed. In a practical system, as the
wavelengths of the lasers are influenced by such factors as a
change of a driving current, fluctuation of temperatures, and
resonator aging, outputted wavelengths will drift in a certain
range. Such uncertain changes of the wavelengths will bring
relatively large influence to the multicarrier optical
communications system, which are mainly embodied as: 1) neighboring
channel crosstalk occurs between subcarrier channels; and 2) edge
subcarriers are subjected to more severe distortion.
An efficient channel spacing monitoring method is important means
for overcoming laser wavelength drifting. On a basis of performing
channel spacing monitoring, feedback adjustment may be performed on
the wavelengths of the lasers, so as to avoid large changes of the
wavelengths, thereby achieving locking of the channel wavelengths.
Stable channel wavelengths may not only avoid neighboring channel
crosstalk, but also make spectral resources to be utilized
efficiently, thereby increasing spectral utilization.
It should be noted that the above description of the background is
merely provided for clear and complete explanation of the present
disclosure and for easy understanding by those skilled in the art.
And it should not be understood that the above technical solution
is known to those skilled in the art as it is described in the
background of the present disclosure.
SUMMARY
Additional aspects and/or advantages will be set forth in part in
the description which follows and, in part, will be apparent from
the description, or may be learned by practice of the
invention.
It was found by the inventor in the implementation of the present
disclosure that the channel spacing monitoring is a basis for
achieving channel wavelength locking, and is also efficient means
for further optimizing a multichannel optical communications
system. During performing the wavelength monitoring, it is not
expected to introduce extra hardware overhead, hence, attention is
paid to a wavelength monitoring scheme based on digital signal
processing performed in a receiver.
Embodiments of the present disclosure provide an apparatus and
method for detecting channel spacing and a system, in which
information on channel spacing is obtained based on performing
signal processing in an optical receiver without introducing extra
large complexity.
According to a first aspect of the embodiments of the present
disclosure, there is provided an apparatus for detecting channel
spacing. The apparatus includes a first estimating unit configured
to estimate a frequency offset of a center channel according to a
received signal, a second estimating unit configured to estimate a
frequency offset of a neighboring channel according to the received
signal, and a determining unit configured to determine channel
spacing according to the frequency offset of the center channel
estimated by the first estimating unit and the frequency offset of
the neighboring channel estimated by the second estimating
unit.
According to a second aspect of the embodiments of the present
disclosure, there is provided a method for detecting channel
spacing. The method includes estimating a frequency offset of a
center channel according to a received signal, estimating a
frequency offset of a neighboring channel according to the received
signal, and determining channel spacing according to the estimated
frequency offset of the center channel and the estimated frequency
offset of the neighboring channel.
According to a third aspect of the embodiments of the present
disclosure, there is provided a multichannel optical receiver,
including the apparatus for detecting channel spacing described in
the first aspect.
According to a fourth aspect of the embodiments of the present
disclosure, there is provided a multichannel optical communications
system, including a transmitter and the optical receiver described
in the third aspect.
An advantage of the embodiments of the present disclosure exists in
that with the embodiments of the present disclosure, estimation
accuracy of channel spacing may be ensured, and influence of
non-ideal factors on estimation performance may be reduced.
With reference to the following description and drawings, the
particular embodiments of the present disclosure are disclosed in
detail, and the principle of the present disclosure and the manners
of use are indicated. It should be understood that the scope of the
embodiments of the present disclosure is not limited thereto. The
embodiments of the present disclosure contain many alternations,
modifications and equivalents within the spirits and scope of the
terms of the appended claims.
Features that are described and/or illustrated with respect to one
embodiment may be used in the same way or in a similar way in one
or more other embodiments and/or in combination with or instead of
the features of the other embodiments.
It should be emphasized that the term "comprise/include" when used
in this specification is taken to specify the presence of stated
features, integers, steps or components but does not preclude the
presence or addition of one or more other features, integers,
steps, components or groups thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
The drawings are included to provide further understanding of the
present disclosure, which constitute a part of the specification
and illustrate the preferred embodiments of the present disclosure,
and are used for setting forth the principles of the present
disclosure together with the description. It is obvious that the
accompanying drawings in the following description are some
embodiments of the present disclosure only, and a person of
ordinary skill in the art may obtain other accompanying drawings
according to these accompanying drawings without making an
inventive effort. In the drawings:
FIG. 1 is a schematic diagram of a structure of the apparatus for
detecting channel spacing of an embodiment of the present
disclosure;
FIG. 2 is a schematic diagram of principles of estimation of
channel spacing;
FIG. 3 is a schematic diagram of operational principles of an
implementation of a preprocessing unit;
FIG. 4 is a schematic diagram of operational principles of another
implementation of the preprocessing unit;
FIG. 5 is a schematic diagram of principles of setting a filter
bandwidth of a center channel;
FIG. 6 is a schematic diagram of principles of setting a filter
bandwidth of a neighboring channel;
FIG. 7 is a schematic diagram of a structure of an implementation
of a second filtering module;
FIG. 8 is a schematic diagram of principles of a spectral
information acquiring module;
FIG. 9 is a schematic diagram of principles of a cutoff frequency
selecting module;
FIG. 10 is a flowchart of the method for detecting channel spacing
of an embodiment of the present disclosure;
FIG. 11 is a schematic diagram of a hardware structure of the
optical receiver of an embodiment of the present disclosure;
and
FIG. 12 is a schematic diagram of a structure of the multichannel
optical communications system of an embodiment of the present
disclosure.
DETAILED DESCRIPTION
These and further aspects and features of the present disclosure
will be apparent with reference to the following description and
attached drawings. In the description and drawings, particular
embodiments of the disclosure have been disclosed in detail as
being indicative of some of the ways in which the principles of the
disclosure may be employed, but it is understood that the
disclosure is not limited correspondingly in scope. Rather, the
disclosure includes all changes, modifications and equivalents
coming within the spirit and terms of the appended claims. Various
embodiments of the present disclosure shall be described below with
reference to the accompanying drawings.
Embodiments of the present disclosure provide an apparatus and
method for detecting channel spacing and a system, in which
information on the optical receiver is used to perform frequency
offset estimation on a center channel and a neighboring channel in
the receiver, so as to achieve judgment of the channel spacing.
Furthermore, necessary processing may be performed on the
information on the receiver, so as to improve a detection accuracy
of the channel spacing. A core content of the embodiments of the
present disclosure is to use an existing or newly-proposed
frequency offset estimation method to perform channel spacing
detection. Efficient receiver data processing not only is a basis
for achieving a function of channel spacing detection, but also
facilitates further improving a detection accuracy, thereby
providing instructions for production of channel control
modules.
The embodiments of the present disclosure shall be described below
with reference to the accompanying drawings and particular
implementations.
Embodiment 1
An embodiment of the present disclosure provides an apparatus for
detecting channel spacing, applicable to an optical receiver of a
multichannel optical communications system. FIG. 1 is a schematic
diagram of a structure of the apparatus. Referring to FIG. 1, the
apparatus 100 includes: a first estimating unit 101, a second
estimating unit 102 and a determining unit 103. In this embodiment,
the first estimating unit 101 is configured to estimate a frequency
offset of a center channel according to a received signal, the
second estimating unit 102 is configured to estimate a frequency
offset of a neighboring channel according to the received signal,
and the determining unit 103 is configured to determine channel
spacing according to the frequency offset of the center channel
estimated by the first estimating unit 101 and the frequency offset
of the neighboring channel estimated by the second estimating unit
102.
FIG. 2 is a schematic diagram of principles the apparatus for
detecting channel spacing of this embodiment. As shown in FIG. 2,
within a bandwidth range of an optical receiver, in addition to a
center channel needing to be demodulated, information on left and
right neighboring channels received simultaneously is further
included. As the bandwidth of the optical receiver is limited, the
information on left and right neighboring channels is only
partially received, which is reflected by a range shown by
broadened solid lines in FIG. 2. Within this range, as spectra of
the neighboring channels are incomplete, spacing between central
wavelengths of two channels cannot be judged directly. In this
embodiment, a method for measuring frequency offsets of the center
channel and a neighboring channel is employed to indirectly measure
the channel spacing.
As shown in FIG. 2, a frequency offset is defined as a difference
between a central frequency and a zero frequency of a channel. In
this embodiment, the first estimating unit 101 and the second
estimating unit 102 respectively estimate the frequency offset of
the center channel (i.e. frequency offset 1 in FIG. 2) and the
frequency offset of the neighboring channel (i.e. frequency offset
2 in FIG. 2), hence the determining unit 103 obtains the channel
spacing based on the difference between frequency offset 2 and
frequency offset 1.
In this embodiment, frequency offset estimation methods used by the
first estimating unit 101 and the second estimating unit 102 are
not limited, and existing frequency offset estimation methods may
be applicable to this embodiment. And the first estimating unit 101
and the second estimating unit 102 may use identical or different
frequency offset estimation methods.
In an implementation, the first estimating unit 101 and the second
estimating unit 102 may estimate respective frequency offsets of
the center channel and the neighboring channel according to formula
(1) below: .DELTA.f=angle(<S.sub.nS.sub.n+k*>)/2.pi.kT.sub.s
(1); where, S.sub.n is complex information of an n-th sampling
point, S.sub.n+k* is complex conjugate information of an (n+k)-th
sampling point, and T.sub.s is a sampling period.
In this implementation, the frequency offset estimation is to find
a relation of a change of a phase offset of a sampling sequence
along with the time. For example, a receiving sampling sequence is
denoted as: S.sub.n={tilde over
(S)}(nT.sub.s)exp(j2.pi..DELTA.fnT.sub.S+.phi.)+N(nT.sub.S); where,
{tilde over (S)}(nT.sub.S) is a signal sequence taking no frequency
offset and phase noise into account, .DELTA.f is a frequency
offset, .phi. is a phase noise (deemed as being of a fixed value in
a certain period of time), and N(nT.sub.S) is a sampling point
noise.
In order to eliminate the influence of the phase noise and the
sampling point noise, the following formula is taken as an
estimated metric in a frequency offset estimation method:
<S.sub.nS.sub.n+k*>=<{tilde over (S)}(nT.sub.S){tilde over
(S)}((n+k)T.sub.S)>exp(j2.pi..DELTA.fT.sub.S); where, <>
denotes calculating an average value, and ()* denotes complex
conjugate.
Thus, the frequency offset .DELTA.f may be expressed by formula
(1).
In another implementation, the first estimating unit 101 and the
second estimating unit 102 may estimate respective frequency
offsets of the center channel and the neighboring channel according
to formula (2) below:
.DELTA.f=angle(<S.sub.nS.sub.n+N*>)/2.pi.NT.sub.S (2); where,
S.sub.n is complex information of an n-th symbol of a periodic
signal or a periodic training sequence, S.sub.n+N* is complex
conjugate information of an (n+N)-th symbol, T.sub.s is a symbol
period, and N is the number of symbols of each period.
In this implementation, it is assumed that the training sequence
{tilde over (S)}(nT.sub.S) used for estimating the frequency offset
is a periodic sequence of a period of N symbols, and N symbols of
each period are random sequences or CAZAC (constant amplitude zero
auto-correlation) sequences, that is, {tilde over
(S)}(nT.sub.S)={tilde over (S)}(n+N)T.sub.S]. Taking the frequency
offsets and the noises into account, a sampling sequence of a
received signal is expressed as: S.sub.n={tilde over
(S)}(nT.sub.S)exp(j2.pi..DELTA.fnT.sub.S+.phi.)+N(nT.sub.S); where,
{tilde over (S)}(nT.sub.S) is a signal sequence taking no frequency
offset and phase noise into account, .DELTA.f is a frequency
offset, .phi. is a phase noise (deemed as being of a fixed value in
a certain period of time), and N(nT.sub.S) is a sampling point
noise.
In order to eliminate the influence of the phase noise and the
sampling point noise, the following formula is taken as an
estimated metric in a frequency offset estimation method:
.times..function..function..times..times..times..pi..DELTA..times..times.-
.times..function..times..function..pi..times..times..times..times..DELTA..-
times..times. ##EQU00001## where, <> denotes calculating an
average value, and ()* denotes complex conjugate.
Thus, the frequency offset .DELTA.f may be expressed by formula
(2).
The above two implementations of frequency offset estimation are
illustrative only, and as described above, this embodiment is not
limited thereto.
In this embodiment, the received signal is a signal received from
the optical receiver, and as a receiving bandwidth of the optical
receiver is limited, the received signal in spectrum includes a
complete channel signal (a signal of the center channel) and two
incomplete signals (signals of the left and right neighboring
channels). On the one hand, the optical receiver normally processes
the received signal, such as photoelectric conversion,
digital-to-analog conversion, demodulation and decoding, etc. And
on the other hand, the optical receiver estimates the channel
spacing by using the apparatus for detecting channel spacing of
this embodiment according to the received signal.
In an implementation of this embodiment, in order to ensure the
frequency offset estimation accuracy, reduce influence of non-ideal
factor on estimation value, so as to facilitate subsequent
frequency offset estimation, the received signal may be
preprocessed before estimating the frequency offsets of the center
channel and the neighboring channel. In this implementation, the
apparatus 100 for detecting channel spacing may further include a
preprocessing unit 104. As shown in FIG. 1, the preprocessing unit
104 is configured to preprocess the received signal, so that the
first estimating unit 101 and the second estimating unit 102
estimate the frequency offset of the center channel and the
frequency offset of the neighboring channel according to the
preprocessed received signal.
In this implementation, the preprocessing of the receive signal may
be, for example, processing of noise suppression (IQ imbalance
elimination), polarization demultiplexing, and pre-equalization,
etc; however, this embodiment is not limited thereto. Two
implementations of the preprocessing unit 104 are provided
below.
FIG. 3 is a schematic diagram of an implementation of the
preprocessing unit 104. In this implementation, the preprocessing
unit 104 includes a first eliminating module 301 configured to
perform IQ imbalance elimination on one path of signal of the
received signal, so as to obtain a preprocessed received signal. As
shown in FIG. 3, the received signal includes H path and V path
signals. As frequency offset estimation needs to be performed only
on one path of signal, in this implementation, one of the H path
and V path signals is discarded, and the other path of signal is
reserved and performed IQ imbalance elimination, which is taken as
output of the preprocessing unit 104.
FIG. 4 is a schematic diagram of another implementation of the
preprocessing unit 104. In this implementation, the preprocessing
unit 104 includes a second eliminating module 401, a third
eliminating module 402 and a processing module 403. The second
eliminating module 401 performs IQ imbalance elimination on one
path signal of the received signal, the third eliminating module
402 performs IQ imbalance elimination on the other path signal of
the received signal, and the processing module 403 performs
polarization demultiplexing and/or pre-equalization on the two
paths of signals processed by the second eliminating module 401 and
the third eliminating module 402, selects one path of the processed
signals, and takes it as the preprocessed received signal. As shown
in FIG. 4, the received signal includes H path and V path signals.
In the optical receiver, IQ imbalance elimination, polarization
demultiplexing and pre-equalization may be performed in succession,
then one of the H path and V path signals is discarded, and the
other path of signal is reserved and taken as output of the
preprocessing unit 104.
The above two implementations of preprocessing are illustrative
only, and other methods for preprocessing a received signal may
also be applicable to this embodiment.
In another implementation of this embodiment, in order to eliminate
influence of other channels and ensure accuracy and frequency
offset estimation accuracy of the center channel and the
neighboring channel, a necessary filtering operation may be
performed on the received signal before estimating the frequency
offsets of the center channel and the neighboring channel. In this
implementation, the apparatus 100 for detecting channel spacing may
further include a filtering unit 105. As shown in FIG. 1, the
filtering unit 105 is configured to filter the received signal, so
that the first estimating unit 101 and the second estimating unit
102 estimate the frequency offset of the center channel and the
frequency offset of the neighboring channel according to the
filtered received signal.
In this implementation, in order to estimate the frequency offsets
of the center channel and the neighboring channel respectively,
different filtering processing may be performed on the center
channel and the neighboring channel, so as to ensure in principle
that an outputted signal of the filtering operation contains only
interested information on channels as possible, thereby eliminating
other channel crosstalk to a maximum extent.
As shown in FIG. 1, in this implementation, the filtering unit 105
may include a first filtering module 1051 and a second filtering
module 1052. The first filtering module 1051 is configured to set a
filter bandwidth of the center channel, filter the received signal
according to the filter bandwidth of the center channel, and
provide the filtered signal to the first estimating unit 101; and
the second filtering module 1052 is configured to set filter
bandwidths of the neighboring channel, filter the received signal
according to the filter bandwidth of the neighboring channel, and
provide the filtered signal to the second estimating unit 102.
FIG. 5 is a schematic diagram of a setting a filter bandwidth of
the center channel. As shown in FIG. 5, a particular numeral value
of the filter bandwidth of the center channel may be determined by
a spectral width of the center channel, and a roll-off factor, etc.
In this implementation, the filter bandwidth of the center channel
may be 0.6 time symbol rate (a Baud rate) of a single-side
bandwidth as an example.
FIG. 6 is a schematic diagram of setting a filter bandwidth of a
neighboring channel. As shown in FIG. 6, principle of setting the
filter bandwidth of the neighboring channel is: ensuring that
information on the neighboring channel is maintained and
information on the center channel is removed in a case where the
channel spacing or the frequency offset change. In this
implementation, the filter bandwidth of the neighboring channel may
be 0.4 time symbol rate (a Baud rate).
In an implementation of the second filtering module 1052, as shown
in FIG. 7, the second filtering module 1052 includes a spectral
information acquiring module 701 and a cutoff frequency selecting
module 702. The spectral information acquiring module 701 is
configured to perform fast Fourier transformation (FFT) on the
received signal, and perform a smoothening operation on a power
spectrum, and the cutoff frequency selecting module 702 is
configured to select a cutoff frequency of high-pass filter of the
neighboring channel.
FIG. 8 is a schematic diagram of operational principles of the
spectral information acquiring module 701. As shown in FIG. 8, the
received signal is a sampling sequence of MxN points extracted from
the receiver. Its spectrum is as shown in the left part in FIG. 8,
which reflects a channel shape; however, as randomness of a data
signal, the spectrum fluctuates to a large extent. As the
measurement of the channel spacing needs only envelope information
of the spectrum, the random data information of the spectrum may be
removed. In the spectral information acquiring module 701,
influence of the random data may be eliminated by using an average
method. First, the sampling sequence of M.times.N points may be
converted into subsequences of M sections via serial/parallel
conversion, each section having N points, each section of
subsequences is performed fast Fourier transformation, so as to
calculate its spectrum. Then, modulo square of each section of
spectrum is calculated, so as to reflect a power spectrum shape in
a frequency domain. Finally, an average power spectrum is
calculated by using the M sections of power spectra. In this way,
the random information on each section of spectrum may be
efficiently suppressed after calculation of the average, an
outputted smooth power spectrum being as shown in the right part in
FIG. 8.
FIG. 9 is a schematic diagram of principles of the cutoff frequency
selecting module 702. As shown in FIG. 9, based on the result
outputted by the spectral information acquiring module 701, a
lowest point of the power spectrum may be searched at the left half
of the spectrum shown in FIG. 9, and the lowest point is taken as a
differential point of the center channel and the neighboring
channel, the left parts to this point being identified as the
neighboring channel, and the right part being identified as the
center channel. Thus, the high-pass filter may be set according to
a frequency of this point, so as to select the neighboring
channel.
The above implementation of the filtering operation is illustrative
only, and other methods for performing a filtering operation on the
received signal are also applicable to this embodiment.
In another implementation of this embodiment, in order to obtain a
feature of the above received signal, a synchronization operation
may be performed on the received signal before estimating the
frequency offsets of the center channel and the neighboring
channel. In this implementation, the apparatus 100 for detecting
channel spacing may further include a synchronizing unit 106. As
shown in FIG. 1, the synchronizing unit 106 is configured to
perform synchronization operations on the received signal, so that
the first estimating unit 101 and the second estimating unit 102
estimate the frequency offset of the center channel and the
frequency offset of the neighboring channel according to the
synchronized received signal.
In this implementation, in order to respectively estimate the
frequency offset of the center channel and the frequency offset of
the neighboring channel, different synchronization operations may
be performed on the center channel and the neighboring channel. As
shown in FIG. 1, in this implementation, the synchronizing unit 106
may include a first synchronizing module 1061 and a second
synchronizing module 1062. The first synchronizing module 1061 is
configured to perform a first synchronization operation on the
received signal and provide a synchronization result to the first
estimating unit 101, so that the first estimating unit 101
estimates the frequency offset of the center channel according to
the synchronized received signal. And the second synchronizing
module 1062 is configured to perform a second synchronization
operation on the received signal and provide a synchronization
result to the second estimating unit 102, so that the second
estimating unit 102 estimates the frequency offset of the
neighboring channel according to the synchronized received
signal.
In this implementation, synchronization methods employed by the
first synchronizing module 1061 and the second synchronizing module
1062 are not limited, and all the currently existing
synchronization methods may be applicable to this embodiment. And
the first synchronizing module 1061 and the second synchronizing
module 1062 may use identical or different synchronization
methods.
In an implementation, the synchronization operation may be:
calculating a correlation value of former N.sub.f sampling values
and latter N.sub.f sampling values of n sections of sampling values
of lengths of 2 N.sub.f at each polarization state starting from
each sampling point according to length N.sub.f of a training
sequence and lengths of cyclic prefix and cyclic postfix set before
and after the training sequence; calculating a square of a modulus
of the correlation value; performing weighted averaging on
predetermined sampling point sequence numbers by using the squares
of moduli of the correlation values at two polarization states, so
as to obtain a starting position of the training sequence; and
determining a position of the training sequence in the received
signal according to the starting position and a length of the
training sequence. As the above method and the above training
sequence are used for the synchronization, the synchronization
accuracy is improved.
In this embodiment, it is taken as an example that the apparatus
for detecting channel spacing is applicable to the optical receiver
of the multicarrier optical communications system to estimate the
channel spacing of the subcarriers. However, this embodiment is not
limited to a multicarrier optical communications system only, and
other systems or apparatuses related to estimation of channel
spacing may also employ the apparatus for detecting channel spacing
of this embodiment.
With the apparatus for detecting channel spacing of this
embodiment, estimation accuracy of channel spacing may be ensured,
and influence of non-ideal factors on estimation value may be
reduced.
Embodiment 2
An embodiment of the present disclosure provides a method for
detecting channel spacing, applicable to an optical receiver of a
multichannel optical communications system. As principles of the
method for solving problems are similar to that of the apparatus in
Embodiment 1, the implementation of the apparatus in Embodiment 1
may be referred to for implementation of the method, with identical
contents being not going to be described herein any further.
FIG. 10 is a flowchart of the method for detecting channel spacing
of this embodiment. Referring to FIG. 10, the method includes:
step 1001: a frequency offset of a center channel is estimated
according to a received signal;
step 1002: a frequency offset of a neighboring channel is estimated
according to the received signal; and
step 1003: channel spacing is determined according to the estimated
frequency offset of the center channel and the estimated frequency
offset of the neighboring channel.
In an implementation, the method may further include: preprocessing
the received signal, so as to estimate the frequency offset of the
center channel and the frequency offset of the neighboring channel
according to the preprocessed received signal. The preprocessing
method is not limited in this embodiment, and any existing
preprocessing methods may be applicable to this implementation.
In an implementation, the method may further include: filtering the
received signal, so as to estimate the frequency offset of the
center channel and the frequency offset of the neighboring channel
according to the filtered received signal.
In this implementation, the filtering the received signal may
include: setting a filter bandwidth of the center channel,
filtering the received signal according to the filter bandwidth of
the center channel, so as to obtain a filtered signal, so as to
estimate the frequency offset of the center channel according to
the filtered signal. And the filtering the received signal may
further include: setting filter bandwidth of the neighboring
channel, filtering the received signal according to the filter
bandwidth of the neighboring channel, so as to obtain a filtered
signal, so as to estimate the frequency offset of the neighboring
channel according to the filtered signal. The filtering operation
is not limited in this embodiment, and identical or different
filtering methods may be used for the center channel and the
neighboring channel. And any existing filtering methods may be
applicable to this implementation.
In this implementation, the filter bandwidth of the center channel
may be determined by a spectral width of the center channel and a
roll-off factor. And the filter bandwidth of the neighboring
channel may ensure that information on the neighboring channel is
maintained and information on the center channel is removed in a
case where the channel spacing or the frequency offset change.
In an implementation, the method may further include: performing
synchronization operations on the received signal, so as to
estimate the frequency offset of the center channel and the
frequency offset of the neighboring channel according to the
synchronized received signal.
In this implementation, a first synchronization operation may be
performed on the received signal, so as to estimate the frequency
offset of the center channel according to the synchronized received
signal, and a second synchronization operation may be performed on
the received signal, so as to estimate the frequency offset of the
neighboring channel according to the synchronized received signal.
The first synchronization operation and the second synchronization
operation are not limited in this embodiment. The first
synchronization operation and the second synchronization operation
may use identical or different synchronization methods, and any
existing synchronization methods may be applicable to this
implementation.
In this embodiment, the above preprocessing, filtering operation
and synchronization operation are all performed before the
estimation of the frequency offsets. And before performing the
estimation of the frequency offsets, any of the preprocessing,
filtering operation and synchronization or a combination thereof
may be performed, and in addition to the above preprocessing,
filtering operation and synchronization, other necessary processing
may be performed in the received signal, which shall not be
described herein any further.
In this embodiment, the frequency offset of the center channel may
be estimated according to formula (1) or formula (2); and likewise,
the frequency offset of the neighboring channel may also be
estimated according to formula (1) or formula (2) as described
above, which shall not be described herein any further.
With the method of this embodiment, estimation accuracy of channel
spacing may be ensured, and influence of non-ideal factors on
estimation value may be reduced.
Embodiment 3
An embodiment of the present disclosure provides a multichannel
optical receiver, including the apparatus for detecting channel
spacing described in Embodiment 1.
FIG. 11 is a schematic diagram of a structure of the optical
receiver of this embodiment. As shown in FIG. 11, the optical
receiver 1100 may include a central processing unit (CPU) 1101 and
a memory 1102, the memory 1102 being coupled to the central
processing unit 1101. It should be noted that this figure is
illustrative only, and other types of structures may also be used,
so as to supplement or replace this structure and achieve
telecommunications function or other functions.
In an implementation, the functions of the apparatus for detecting
channel spacing described in Embodiment 1 may be integrated into
the central processing unit 1101.
In another implementation, the apparatus for detecting channel
spacing and the central processing unit 1101 may be configured
separately. For example, the apparatus for detecting channel
spacing may be configured as a chip connected to the central
processing unit 1101, with its functions being realized under
control of the central processing unit 1101.
As shown in FIG. 11, the optical receiver 1100 may further include
a communication module 1103, an input unit 1104, a local laser
1105, a display 1106 and a power supply 1107. It should be noted
that the optical receiver 1100 does not necessarily include all the
parts shown in FIG. 11. And furthermore, the optical receiver 1100
may include components not shown in FIG. 11, and the related art
may be referred to.
As shown in FIG. 11, the central processing unit 1101 is sometimes
referred to as a controller or control, and may include a
microprocessor or other processor devices and/or logic devices. The
central processing unit 1101 receives input and controls operations
of every components of the optical receiver 1100.
In this embodiment, the memory 1102 may be, for example, one or
more of a buffer memory, a flash memory, a hard drive, a mobile
medium, a volatile memory, a nonvolatile memory, or other suitable
devices, which may store predefined or preconfigured information.
Furthermore, it may store programs executing related information.
And the central processing unit 1101 may execute the programs
stored in the memory 1102, so as to realize configuration
information and reconfiguration information storage, etc. Functions
of other parts are similar to those of the related art, which shall
not be described herein any further. The parts of the optical
receiver 1100 may be realized by specific hardware, firmware,
software, or any combination thereof, without departing from the
scope of the present disclosure.
The optical receiver of the embodiment of the present disclosure
may ensure estimation accuracy of channel spacing, and reduce
influence of non-ideal factors on estimation value.
Embodiment 4
An embodiment of the present disclosure provides a multichannel
optical communications system. FIG. 12 is a schematic diagram of a
structure of the system. As shown in FIG. 12, the system 1200
includes a transmitter 1201 and an optical receiver 1202. In this
embodiment, the optical receiver 1202 may be realized by the
optical receiver described in Embodiment 3, the contents of which
being incorporated herein, and being not going to be described
herein any further.
With the multichannel optical communications system provided by the
embodiment of the present disclosure, estimation accuracy of
channel spacing may be ensured, and influence of non-ideal factors
on estimation value may be reduced.
An embodiment of the present disclosure provides a
computer-readable program, wherein when the program is executed in
an apparatus for detecting channel spacing or an optical receiver,
the program enables the apparatus or the optical receiver to carry
out the method for detecting channel spacing as described in
Embodiment 2.
An embodiment of the present disclosure further provides a storage
medium in which a computer-readable program is stored, wherein the
computer-readable program enables an apparatus for detecting
channel spacing or an optical receiver to carry out the method for
detecting channel spacing as described in Embodiment 2.
The above apparatuses and methods of the present disclosure may be
implemented by hardware, or by hardware in combination with
software. The present disclosure relates to such a
computer-readable program that when the program is executed by a
logic device, the logic device is enabled to carry out the
apparatus or components as described above, or to carry out the
methods or steps as described above. The present disclosure also
relates to a storage medium for storing the above program, such as
a hard disk, a floppy disk, a CD, a DVD, and a flash memory,
etc.
The present disclosure is described above with reference to
particular embodiments. However, it should be understood by those
skilled in the art that such a description is illustrative only,
and not intended to limit the protection scope of the present
disclosure. Various variants and modifications may be made by those
skilled in the art according to the spirits and principle of the
present disclosure, and such variants and modifications fall within
the scope of the present disclosure.
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